Management of Hypernatraemia

Serum Na >146mmol/L can be caused by reduced water intake (dehydration), or where water losses are greater than sodium losses (e.g. watery diarrhoea).

Assessment / Monitoring

• There are no specific clinical features of hypernatraemia. It is usually diagnosed incidentally on serum testing. Also check other biochemical indices such as renal failure, hyperglycaemia and hypercalcaemia.
• Identify underlying cause of hypernatraemia. Consider measuring urine osmolality.
  • Urine osmolality < plasma osmolality – look for diabetes insipidus
  • Urine osmolality > plasma osmolality – look for osmotic diuresis / heatstroke, etc.
• If patient is also hypovolaemic, then monitor urinary output and renal function.

General Management

• Treat underlying cause once identified. This is as important as treatment of hypernatraemia.
• Mild cases of hypernatraemia - replace missing body water with oral water (not electrolyte drinks) or glucose 5% IV.
• Severe cases of hypernatraemia (e.g. Na >170mmol/L) – give glucose 5% IV unless the patient is volume depleted and hypotensive, in which case give sodium chloride 0.9% IV. It is important that the rate of reduction of serum Na does not occur more rapidly than about 10mmol/L per day.
  • Reassess and record patient's blood results and clinical conditions every 8 hours. Recheck serum Na after 2 L of fluid replacement, or after 8 hours at the latest.
  • Patients should be handed over to the next shift to clarify monitoring and fluid requirements.
• If diabetes is simultaneously present, then BM monitoring is required and if the blood glucose is >30mmol/L then follow HONC guideline.
• In complex cases, the free water deficit can be calculated and advice can be sought from Biochemistry physicians, to guide the rate of water replacement.

Guideline last reviewed June 2021.